docs: add comprehensive testing and verification guide

Created complete testing documentation and verification script:

📚 TESTING_GUIDE.md (Comprehensive):
- Quick test checklist (5 essential commands)
- Step-by-step detailed verification
- Log output verification
- Integration test examples
- Manual verification checklist
- One-click verification script
- Debugging tips
- Performance comparison tests
- Common troubleshooting

🔧 verify-changes.sh (Automation):
- Automated verification script
- 4 verification steps:
  1. Spring Java Format validation
  2. Core unit tests
  3. All module tests
  4. Module build
- Colored output for clear results
- Auto-suggestions on failures
- Exit codes for CI/CD

Usage:
  # Manual step-by-step
  Follow TESTING_GUIDE.md

  # Automated one-click
  ./verify-changes.sh

Benefits:
✅ Self-service testing capability
✅ Clear success/failure indicators
✅ Actionable error messages
✅ Suitable for all contributors
✅ CI/CD friendly

Perfect for:
- Contributors validating their changes
- PR reviewers checking submissions
- Automated testing pipelines

Related: 6fee05b, 47906be, 71f9191

Author: JGoP-L